Golf ball

ABSTRACT

A golf ball formed of multiple layers that allows limiting an uplifting trajectory, providing a trajectory in which the height of the golf ball is well retained in the latter half of the flight of the ball thereby increasing travel distance, where at least one layer is made of a composition of a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound mixed together, at least 80% of the carboxyl group contained in the composition is neutralized, and the total volume of the dimples (Dv) on the cover surface ranges from 495 to 575 mm 3 . The above composition is suitable for the cover. The higher fatty acid is a fatty acid with 12 to 40 carbon atoms, and preferably is stearic acid or oleic acid.

This nonprovisional application is based on Japanese Patent Application No. 2003-300319 filed with the Japan Patent Office on Aug. 25, 2003, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf ball that eliminates the decrease in travel distance caused by an uplifting trajectory, particularly the decrease in distance against an opposing wind.

2. Description of the Background Art

Conventionally, a common resin component for the cover of a golf ball is ionomer resin of ethylene-(meth-)acrylic acid copolymer, which possesses good durability against impact and high cut resistance and thus is widely used as cover material for two-piece and thread-wound golf balls. However, a golf ball with a cover made of an ionomer resin has a feel that is harder than that of a golf ball with a balata cover and allows less control due to the difficulties in producing spin when struck by an iron club. Golf balls with a balata cover are widely used by advanced and professional players because of its superior feel and control. They are produced, however, in a complex manufacturing process and has a lower cut resistance. Thus, a variety of alternative soft covers substituting for balata covers have been proposed in recent years.

For example, U.S. Pat. No. 4,884,814 discloses a technique that uses soft ionomer resin for the base resin of a cover. The technique provides a soft/hard ionomer blend cover made of ethylene-(meth-)acrylic acid-(meth-)acrylate terpolymer, a relatively soft ionomer resin, that is blended, to some degree, with a binary copolymer ionomer resin of ethylene-(meth-)acrylic acid copolymer. The technique provides improvement in feel and control, in terms of which a conventional golf ball with a cover made of ionomer resin of ethylene-(meth-)acrylic acid copolymer exhibited poor performances.

The soft/hard ionomer blend cover according to the above technique is soft and thus facilitates spinning the ball when struck by an iron club, however, it increases friction between the club face and the cover such that a ball using a hard core material, particularly a two piece solid golf ball, may have its cover surface chipped away by the grooves of an iron club, resulting in ragged ball surface. This ionomer cover has a low hardness that reduces the impact resilience of the cover, and thus of the ball itself.

To reduce the abrasion of an ionomer cover caused by the impact by an iron club, GB 2 264 302 proposes a cover made of a metal salt of two or more kinds of ethylene-unsaturated carboxylic acid-unsaturated carboxylate ternary copolymer with low flexural modulus. This technique, however, does not provide a sufficient abrasion resistance and impact resilience when struck by an iron club.

GB 2 311 530 proposes a golf ball characterized in that the base resin of a cover is mainly formed of the following three components that are heated and mixed: an ionomer resin; an acid-modified thermoplastic elastomer with or without an additional OH group at an end; a styrene-butadiene-styrene block copolymer containing an epoxy group or a styrene-isoprene-styrene block copolymer containing an epoxy group, where the covering composition forming the cover has a flexural rigidity of 50-300 MPa and a Shore D hardness of 40-60. This technique, although providing improved feel (when struck) and control and cut resistance, does not provide satisfactory impact resilience.

US Publication No. US 2003/0013549A1 uses a composition with increased degree of neutralization of carboxylic acid in an ionomer composition for portions of a golf ball other than the cover i.e. the intermediate layer or center, thereby increasing the coefficient of restitution of the golf ball. A composition with increased degree of neutralization of carboxylic acid in an ionomer composition may be used for the center, intermediate layer or cover of a golf ball to provide improved resilience, although this causes increased spin rate, leading to an uplifting trajectory such that the distance, particularly against an opposing wind, decreases significantly, especially when the composition is used for the cover.

SUMMARY OF THE INVENTION

When the center, intermediate layer-or cover of a golf ball is made of a composition with increased degree of neutralization of carboxylic acid in the ionomer composition, especially when the cover is made of the above composition, the golf ball experiences an uplifting trajectory, causing decrease in the travel distance, particularly against an opposing wind. Accordingly, the present invention provides a golf ball with an intermediate layer or cover made of a composition with increased degree of neutralization of carboxylic acid in the ionomer composition and with a total volume of dimples larger than usual in order to limit an uplifting trajectory (a larger drag coefficient) providing a trajectory in which the height of the golf ball is well retained in the latter half of the flight of the ball, thereby increasing the distance.

The present invention provides a golf ball formed of multiple layers, where at least one layer is made of a composition of a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound mixed together, at least 80% of the carboxyl group contained in the composition is neutralized, and the total volume of dimples (Dv) on the cover surface is 495-575 mm³.

Further, the present invention provides a golf ball formed of multiple, layers, where the cover is made of a composition of a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound mixed together, at least 80% of the carboxyl group contained in the composition is neutralized, and the total volume of dimples (Dv) on the cover surface is 495-575 mm³.

Preferably, the higher fatty acid is a higher fatty acid with 12-40 carbon atoms, and is stearic acid or oleic acid. It is desirable that the metal component of the inorganic metal compound is selected from Na, Zn, Mg, Ca, Li and K.

Preferably, the cover is made of a composition with a Shore D hardness of 40-65. The degree of neutralization of the carboxyl group contained in the composition is no less than 90%, particularly preferably 100%.

The present invention provides improved impact resilience by forming the intermediate layer or the cover from a composition with increased degree of neutralization of carboxylic acid in the ionomer composition. The total volume of dimples of a golf ball is larger than usual to enable minimizing the decrease in the distance caused by an uplifting trajectory of the golf ball especially against an opposing wind, providing a trajectory in which the height of the golf ball is well retained in the latter half of the flight of the ball, thereby increasing the distance.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross sectional view of a golf ball.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a golf ball formed of multiple layers, where at least one layer is made of a composition of a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound mixed together, at least 80% of the carboxyl group contained in the composition is neutralized, and the total volume of dimples (Dv) on the cover surface is 495-575 mm³.

Particularly, the composition may be used for the cover to provide a golf ball with excellent resilience.

<Ternary Copolymer Ionomer Composition with Higher Degree of Neutralization>

The present invention uses a ternary copolymer ionomer composition with higher degree of neutralization for at least one of a center, intermediate layer and cover layer of a golf ball.

A ternary copolymer ionomer with higher degree of neutralization as used herein means a composition including a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound that are heated and mixed together, where all the carboxyl group contained in the composition (the carboxyl group in the ternary copolymer ionomer together with the carboxyl group in the higher fatty acid) is neutralized, with the total degree of neutralization being 80% or more. Since a degree of neutralization less than 80% provides an insufficient resilience, the degree of neutralization is preferably 85% or more and more preferably 90% or more, and particularly 100% is optimal.

The degree of neutralization can be determined from the amount of remaining carboxyl group ([COOH]) and the amount of metal salt of carboxylic acid ([COOM]) in accordance with the following formula: The degree of neutralization (%)={[COOM] ([COOH]+[COOM])}×100

The amount of remaining carboxyl group ([COOH]) is measured by heating and melting the ionomer composition into tetrahydrofuran and titrating it in the heated state with a predetermined concentration of potassium hydroxide. The amount of metal salt of carboxylic acid ([COOM]) is measured by analyzing the neutralizing metal. The metal may be analyzed by Hitachi, Ltd. polarized Zeeman atomic absorption spectrophotometer, model 180-80, for example, for monovalent metals such as sodium, and by Seiko Electronics, Ltd., sequential ICP emission spectrophotometer, model SPS1100, for example, for bivalent metals such as zinc.

In the ternary copolymer ionomer composition, higher fatty acid accounts for 20-50 parts by mass, and preferably 25-45 parts by mass per 100 parts of the ternary copolymer ionomer. A loading of higher fatty acid less than 20 parts provides insufficient fluidity of the composition, while a loading more than 50 parts means a decrease in the proportion of the ternary copolymer ionomer component, resulting in low resilience.

Inorganic metal compound accounts for 0.5-10 parts by mass, preferably 1-8 parts. When the inorganic metal compound accounts for less than 0.5 parts, the degree of neutralization is small and cannot provide desired properties. More than 10 parts thereof result in insufficient fluidity of the composition.

The ternary copolymer ionomer composition with higher degree of neutralization may be prepared by mixing a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound, and heating and mixing them at a temperature of 100-250° C. for 1-10 minutes. The ternary copolymer ionomer composition with higher degree of neutralization has a Shore D hardness of 45-60, more preferably 50-58.

<Ternary Copolymer Ionomer>

The ternary copolymer ionomer used in the present invention is an ionomer made of a ternary copolymer of ethylene and α, β unsaturated carboxylic acid and α, β unsaturated carboxylate. Preferably, it is a ternary copolymer of ethylene and (meth-) acrylic acid and (meth-) acrylate.

The α, β unsaturated carboxylate may be a methyl, ethyl, propyl, n-butyl or isobutyl ester of α, β unsaturated carboxylic acid, for example.

The ternary copolymer ionomer has the ethylene component in 45-92 percent by mass, preferably 55-85 percent by mass, and the α, β unsaturated carboxylic acid component in 3-25 percent by mass, preferably 5-20 percent by mass, and the α, β unsaturated carboxylate component in 5-30 percent by mass, preferably 10-25 percent by mass.

In the ternary copolymer of ethylene and (meth-) acrylic acid and (meth-) acrylate, the preferred proportions of the three components in the copolymer composition is: ethylene in 70-85 percent by weight, (meth-) acrylic acid in 5-20 percent by weight, and (meth-) acrylate in 10-25 percent by weight.

Examples of the ternary copolymer ionomer are Hi-milan 1856 (Na), Hi-milan 1855 (Zn), Hi-milan AM 7316 (Zn) and the like, commercially available from Mitsui-Dupont Chemical Co. Ltd. Dupont Co. Ltd. also sells Surlyn 8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn), Surlyn 6320 (Mg), and the like. Also, Exxon Mobil Corp. sells IOTEC 7510 (Zn), IOTEC 7520 (Zn), and the like. With respect to improvement in resilience, Surlyn 6320 (Mg) is preferred. The metals set forth in the parentheses indicate neutralizing metals of the ionomer. The ternary copolymer ionomer preferably has a Shore D hardness in the range from 30 to 60, more preferably from 40 to 58.

<Higher Fatty Acid>

Higher fatty acids used in the present invention are preferably those with 12-40 carbon atoms. A higher fatty acid with less than 12 carbon atoms has an insufficient molecular weight that results in lower resilience, though providing a better fluidity. A higher fatty acid with more than 40 carbon atoms has an excessive molecular weight so that the fluidity tends to be low at high degrees of neutralization. Accordingly, the present invention preferably has 12-40 carbon atoms, and more preferably 14-30, and still more preferably 16-24. Stearic acid, oleic acid and linoleic acid, which have 18 carbon atoms, are particularly preferable. The higher fatty acid may be a saturated or unsaturated fatty acid.

<Inorganic Metal Compound>

The inorganic metal compounds used in the present invention include magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, sodium oxide, sodium carbonate, calcium oxide, calcium hydroxide and lithium hydroxide. Magnesium oxide and magnesium hydroxide are particularly preferable.

The preferred combinations of a higher fatty acid and an inorganic metal compound in the present invention include stearic acid, oleic acid, and magnesium oxide, magnesium hydroxide to improve moldability and resilience.

<Polymer Components in Composition>

The ternary copolymer ionomer composition with higher degree of neutralization of the present invention is preferably mixed with other resin and/or rubber components as required to provide needed properties of the center, intermediate layer, cover.

For example, as for the compositions for the cover, a ternary copolymer ionomer composition with higher degree of neutralization can be constructed of a ternary copolymer ionomer component only, while a ternary copolymer ionomer with a lower degree of neutralization or a binary copolymer ionomer may be used. Examples of binary copolymer ionomers in trade names are Hi-milan 1555 (Na), Hi-milan 1557 (Zn), Hi-milan 1605 (Na), Hi-milan 1706 (Zn), Hi-milan 1707 (Na), Hi-milan AM 7318 (Na), Hi-milanAM7315 (Zn), Hi-milanAM7317 (Zn), Hi-milan AM 7311 (Mg), Hi-milan MK 7320 (K) and the like, all commercially available from Mitsui-Dupont Chemical Co., Ltd.

Dupont Co., Ltd also sells Surlyn 8945 (Na), Surlyn 8940 (Na), Surlyn 9910 (Zn), Surlyn 9945 (Zn), Surlyn 7930 (Li), Surlyn 7940 (Li) and the like.

Also, Exxon Mobil Corp. sells IOTEC 7010 (Zn), IOTEC 8000 (Na), IOTEC 7030 (Zn), IOTEC 8030 (Na) and the like. Na, Zn, K, Li and Mg in the parentheses indicate the metals of these neutralizing metal ions.

According to the present invention, one or more of these ionomer resins may be mixed with the above composition. Also, two or more of ionomer resins neutralized with the illustrated monovalent metal ions and ionomer resins neutralized with the illustrated bivalent metal ions may be mixed for use in the present invention.

Moreover, the polymer components to be mixed with the above composition may include one or more of polyolefin-based elastomers, polyurethane-based elastomers and polyester-based elastomers, for example, that are mixed together. Examples of polyolefin-based elastomers in trade names are Milastomer M4800NW from Mitsui Chemicals, Inc., and Sumitomo TPE3682, 9455 from Sumitomo Chemicals Co., Ltd. Examples of polyurethane-based elastomers in trade names are KU ON 9195, KURAMIRON 9180 from Kuraray Co., Ltd., Elastollan ET880 and ET 890 from BASF Polyurethane Elastomers Ltd. Examples of polyester-based elastomers in trade names are Hytrel 4047, 4767, 5557 from Toray-Dupont Co., Ltd.

Further, polystyrene-based elastomers, such as thermoplastic elastomers containing a styrene block may be used. Thermoplastic elastomers containing a styrene block may be a block copolymer including a styrene block and a unit derived from a conjugated diene compound, and the conjugated diene compound may be one or more of butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and the like, where butadiene, isoprene and a combination thereof is preferred.

Examples of thermoplastic elastomers containing a styrene block are styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butylene-styrene block copolymer (SEBS) where the double bond portion of the butadiene in SBS is hydrogenated, styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-propylene-styrene block copolymer (SEPS) where the double bond portion of the isoprene in SIS is hydrogenated, styrene-isoprene-butadiene-styrene block copolymer (SIBS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) where the double bond portion of the butadiene or isoprene in SIBS is hydrogenated and modifications thereof.

For the cover or intermediate layer, the polymer components stated above may be mixed in 80 parts by mass or less, particularly 50 parts by mass or less, per 100 parts of the ternary copolymer ionomer with higher degree of neutralization.

For the center, conventional center compositions may simultaneously be used. For example, a rubber component may be mixed in 80 parts by mass or less per 100 parts of the ternary copolymer ionomer with higher degree of neutralization. Then, one or more co-crosslinking agents in 10-50 parts by mass in total per 100 parts of the rubber component may be added that are made of a, P-monoethyleric unsaturated carboxylic acid such as acrylic acid, methacrylic acid and the like or its metal salt, or trimethylolpropane trimethacrylate polyfunctional monomer and the like. The rubber component may be polybutadiene, polyisoprene or the like. Further, a filler such as zinc oxide, barium sulfate or the like in 10-30 parts by mass, a peroxide such as dicumyl peroxide in 0.5-5 parts by mass and, if necessary, an antioxidant in 0.1-1 part by mass may be added.

<Other Ingredients>

To the cover composition forming the cover and the like in the present invention may be added a variety of additives as required, such as pigment, weight conditioner, dispersant, ultraviolet absorbent, photo-stabilizer or the like.

<Total Volume of Dimples Dv>

According to the present invention, the total volume of dimples ranges from 495 to 575 mm³. A total volume of dimples less than 495 mm³ cannot limit the uplifting trajectory due to the increased spin rate. More preferably, the total volume is 505 mm³ or more, yet more preferably 515 mm³ or more, particularly preferably 525 mm³ or more. A total volume more than 575 mm³ excessively lowers the trajectory leading to the tendency of the ball to drop, reducing the travel distance. The total volume is more preferably 565 mm³ or less.

“Total volume of dimples-Dv” will now be explained referring to FIG. 1 which is a partial cross section of a golf ball showing a dimple area. “Volume of dimple” means a volume defined by, in FIG. 1, an imaginary spherical surface of a golf ball (i.e. the spherical surface imagined when assuming that dimple 2 does not exist) and the surface of dimple 2. “Volume of dimple” is the sum of an upper volume w and a lower volume V, which are separated from each other by the plane connecting the points P—P at which the imaginary spherical surface crosses the dimple surface. “Total volume of dimples Dv” is defined as the sum of volumes of the dimples provided on the surface of a golf ball, each being represented as “volume of dimple (w+v)”. The diameter of a dimple, d, is defined as the distance between the points P—P at which the imaginary spherical surface crosses the dimple surface. Finally, in FIG. 1, the sphere depth of a dimple is defined as D₀, the dimple depth as D₁.

<Cover Hardness>

According to the present invention, the cover preferably has a Shore D hardness of 40-55, more preferably 42-60, particularly 45-55. A Shore D hardness less than 40 produces an excessively soft cover which results in low resiliency, as well as increased spin rate, causing the travel distance to be decreased. A Shore D hardness more than 65 produces a cover that is excessively hard, which means an inferior feel.

<Structure of Golf Ball and Compositions of its Layers>

According to the present invention, ternary copolymer ionomer with higher degree of neutralization may be used for at least one of the center, intermediate layer and cover. Any of the following modes can achieve the objectives of the present invention.

-   -   a. For a two-layer structure of center (or core)/cover layer,         ternary copolymer ionomer with higher degree of neutralization         may be used for one or both of the center and the cover.     -   b. For a three-layer structure of center/intermediate         layer/cover layer, it may be used for one, two or all of the         center, intermediate layer and cover layer.

Further, it may be used for at least one layer of a golf ball formed of four layers. Particularly, it may be most advantageously used for the cover.

<Method of Manufacturing Golf Ball>

A generally used technique may be applied without limitation to manufacture inventive golf balls. For example, a method that involves preparing ingredients in desired weights and then injection-molding them, or a method that involves press-molding may be used.

<Ball Weight and Ball Outer Diameter>

The diameter of an inventive golf ball ranges from 40 to 45 mm, particularly from 42 to 44 mm. Since the air resistance may be decreased within the range provided in the specifications regulated by the United States Golf Association (USGA), the diameter is preferably 42.67-42.80 mm. The mass of a golf ball according to the present invention ranges from 44 to 46 g, particularly 45.00 g to 45.93 g.

EXAMPLES

Table 1 sets forth center and intermediate layer formulations, while Table 2 sets forth cover formulations. Ternary copolymer ionomer compositions with higher degree of neutralization used for the examples (shown below Tables 1 and 2) are provided. TABLE 1 A B C D E Center Formulation BR18 ※1 100.0 100.0 100.0 100.0 zinc acrylate 33.0 33.0 33.0 33.0 zinc oxide 12.0 7.5 7.5 7.5 diphenyl disulfide ※2 0.5 0.5 0.5 0.5 dicumyl peroxide ※3 0.8 0.8 0.8 0.8 ternary copolymer ionomer 100.0 (Mg 100%) ※7 curing condition 170° C. × 15 min. 170° C. × 15 min. 170° C. × 15 min. 170° C. × 15 min. center diameter (mm) 40 32.5 37 37 40 Intermediate Formulation BR11 ※1 none 100 none layer zinc acrylate 36 zinc oxide 11 diphenyl disulfide ※2 0.5 dicumyl peroxide ※3 0.7 ternary copolyrner ionomer 100 (Mg 100%) ※7 Hi-milan 1605 ※4 30 Hi-milan 1706 ※5 30 Surlyn 6320 ※6 40 curing condition 170° C. × 15 min. core diameter (center/intermediate layer) (mm) 40 40 40 40 40 98-1275N deformation (mm) 3 2.9 2.9 2.8 3 ※1 High cis-polybutadiene from JSR Corporation ※2 From Sumitomo Seika Chemicals Co., Ltd. ※3 From NOF Corporation ※4 Na neutralized binary ionomer from Mitsui-Dupont Chemical Co., Ltd. ※5 Zn neutralized binary ionomer from Mitsui-Dupont Chemical Co., Ltd. ※6 Mg neutralized ternary ionomer from Du Pont Co., Ltd. ※7 Surlyn 6320 mixed with stearic acid, magnesium oxide while heated, and 100% of carboxyl group in stearic acid neutralized by Mg

TABLE 2 1 2 Cover Hi-milan 1605 ※4 50 Formulation Hi-milan 1706 ※5 Surlyn 6320 ※6 50 ternary copolymer ionomer (Mg 100%) ※7 100 titanium oxide  3  3 Shore D Hardness 57D 55D ※5 Zn neutralized binary ionomer from Mitsui-DuPont Chemical Co., Ltd. ※6 Mg neutralized ternary ionomer from Du Pont Co., Ltd. ※7 Surlyn 6320 mixed with stearic acid, magnesium oxide while heated, and 100% of carboxyl group in stearic acid neutralized with Mg Surlyn 6320: 100 parts by mass Stearic acid: 40 parts by mass Magnesium oxide: 3.9 parts by mass

Tables 3 and 4 set forth dimple characteristics. The shown formulations and dimple characteristics were used to fabricate the golf balls of the examples and comparative examples. The golf balls of the examples are illustrated in Table 5 and those of the comparative examples in FIG. 6, each with its property evaluation. TABLE 3 Total Sphere Volume Upper Total upper Sum Ball Diameter Depth depth Curvature V volume V + W volume volume (V + W) diameter Type Number d(mm) D₁(mm) D₀(mm) (mm) (mm³) W (mm³) (mm³) (mm³) (mm³) (mm³) I 42.70 A 132 4.100 0.1325 0.2311 15.92 0.876 0.652 1.528 115.6 86.0 201.6 42.70 B 180 3.550 0.1320 0.2059 12.00 0.654 0.366 1.020 117.8 65.9 183.7 42.70 C 60 3.400 0.1300 0.1978 11.18 0.591 0.308 0.899 35.5 18.5 54.0 42.70 D 60 3.200 0.1300 0.1900 9.91 0.524 0.242 0.765 31.4 14.5 45.9 432 300.3 184.9 485.2 II 42.70 A 132 4.100 0.1410 0.2396 14.97 0.932 0.652 1.584 123.1 86.0 209.1 42.70 B 180 3.550 0.1400 0.2139 11.32 0.694 0.366 1.060 125.0 65.9 190.9 42.70 C 60 3.400 0.1400 0.2078 10.39 0.637 0.308 0.945 38.2 18.5 56.7 42.70 D 60 3.200 0.1400 0.2000 9.21 0.564 0.242 0.806 33.9 14.5 48.4 432 320.1 184.9 505.0 III 42.70 A 132 4.100 0.1500 0.2486 14.08 0.992 0.652 1.644 130.9 86.0 217.0 42.70 B 180 3.550 0.1500 0.2239 10.58 0.744 0.366 1.110 133.9 65.9 199.8 42.70 C 60 3.400 0.1475 0.2153 9.87 0.671 0.308 0.979 40.3 18.5 58.8 42.70 D 60 3.200 0.1450 0.2050 8.90 0.585 0.242 0.826 35.1 14.5 49.6 432 340.2 184.9 525.1

TABLE 4 Total Sphere Volume Upper Total upper Sum Ball Diameter Depth depth Curvature V volume V + W volume volume (V + W) diameter Type Number d(mm) D₁(mm) D₀(mm) (mm) (mm³) W (mm³) (mm³) (mm³) (mm³) (mm³) IV 42.70 A 132 4.100 0.1600 0.2588 13.21 1.058 0.652 1.710 139.7 86.0 225.7 42.70 B 180 3.550 0.1575 0.2314 10.08 0.782 0.366 1.148 140.7 65.9 206.6 42.70 C 60 3.400 0.1550 0.2228 9.40 0.706 0.308 1.013 42.3 18.5 60.8 42.70 D 60 3.200 0.1550 0.2150 8.34 0.625 0.242 0.867 37.5 14.5 52.0 432 360.2 184.9 545.1 V 42.70 A 132 4.100 0.1675 0.2661 12.63 1.108 0.652 1.760 146.3 86.0 232.3 42.70 B 180 3.550 0.1675 0.2414 9.49 0.831 0.366 1.197 149.7 65.9 215.5 42.70 C 60 3.400 0.1650 0.2328 8.84 0.751 0.308 1.059 45.1 18.5 63.6 42.70 D 60 3.200 0.1625 0.2225 7.96 0.656 0.242 0.897 39.3 14.5 53.8 432 380.4 184.9 565.2 VI 42.70 A 132 4.100 0.1760 0.2746 12.03 1.165 0.652 1.816 153.7 86.0 239.8 42.70 B 180 3.550 0.1750 0.2489 9.09 0.869 0.366 1.235 156.4 65.9 222.3 42.70 C 60 3.400 0.1750 0.2428 8.34 0.797 0.308 1.105 47.8 18.5 66.3 42.70 D 60 3.200 0.1750 0.2350 7.40 0.707 0.242 0.948 42.4 14.5 56.9 432 400.4 184.9 585.2

TABLE 5 Examples 1 2 3 4 5 6 Ball Specification Core (center + intermediate layer) formulation A A A A C E Core diameter (mm) 40 40 40 40 40 40 Core 98-1274N deformation (mm) 3.0 3.0 3.0 3.0 2.9 3.0 Cover formulation 2 2 2 2 1 1 Cover thickness (mm) 1.4 1.4 1.4 1.4 1.4 1.4 Cover Shore D hardness 55D 55D 55D 55D 57D 57D Ball 98-1274N deformation (mm) 2.75 2.75 2.75 2.75 2.65 2.75 Ball diameter D (mm) 42.7 42.7 42.7 42.7 42.7 42.7 Dimple specification III II IV V III III Total volume of dimples (mm³) 525 505 545 565 525 525 Ball Resilience 103 103 103 103 102 100 Properties Launch angle (°) 11.5 11.5 11.5 11.5 11.6 11.4 Angle of trajectory (°) 12.7 12.8 12.6 12.5 12.7 12.7 Angle of trajectory - Launch angle (°) 1.2 1.3 1.1 1 1.1 1.3 Total distance 101 101 102 103 101 100

TABLE 6 Comparative Examples 1 2 3 4 5 Ball Specification Core (center + intermediate layer) formulation A B D A A Core diameter (mm) 40 40 40 40 40 Core 98-1274N deformation (mm) 3.0 2.9 2.8 3.0 3.0 Cover formulation 1 1 1 2 2 Cover thickness (mm) 1.4 1.4 1.4 1.4 1.4 Cover Shore D hardness 57D 57D 57D 55D 55D Ball 98-1274N deformation (mm) 2.75 2.65 2.55 2.75 2.75 Ball diameter D(mm) 42.7 42.7 42.7 42.7 42.7 Dimple specification III III III I VI Total volume of dimples (mm³) 525 525 525 485 585 Ball Resilience 99 98 97 103 103 Properties Launch angle (°) 11.5 11.4 11.3 11.4 11.6 Angle of trajectory (°) 12.8 12.7 12.6 13 12.1 Angle of trajectory - Launch angle (°) 1.3 1.3 1.3 1.6 0.5 Total distance 99 98 97 98 97

In the examples of the present invention, ingredients were regulated to produce a center, intermediate layer and cover of desired weights, and the outer diameter and thickness were regulated by injection molding.

<Test Method>

(1) Coefficient of Restitution

The golf balls were struck by a cylindrical aluminum object of 200 g at a speed of 45 m/sec, and the speeds of the cylindrical object and each golf ball before and after the impact were measured, and their speeds and weights were used to calculate the coefficient of restitution of the golf ball. Five measurements were made for each golf ball to determine an average that was used as the value of the ball. Values relative to Example 6 which has the value 100 are shown. A greater value indicates better resilience.

(2) 98-1274N Deformation

Deformation (mm) of a golf ball, core or center was measured beginning with an initial load of 98N applied thereto and ending with a final load of 1274N. A greater number indicates more softness.

(3) Flight Performance

A metal head wood No. 1, a driver, was attached to a swing robot from True Temper. Each golf ball was struck by the golf club at a head speed of 45 m/sec, and launch angle immediately after the shot, angle of trajectory, total travel distance (the distance all the way to the stopping point) were measured. Five measurements were made for each golf ball to determine an average that was used as the value of the ball. The units for the launch angle and the angle of trajectory are “degree”, and total distances relative to Example 6 which has the value 100 are shown, where a greater value indicates greater total distance.

(4) Shore D Hardness

Measurement was conducted in accordance with ASTM-D2240. A heat press-molded sheet with a thickness of about 2 mm made of the above composition was preserved at 23° C. for 2 weeks. Thereafter, three or more stacked sheets were measured using a spring type hardness meter (Shore D type), by an automatic rubber hardness meter model LA1 from Kobunshi Keiki Co., Ltd.

<Test Results>

Comparative Examples 1 to 3 do not contain ternary copolymer ionomer with higher degree of neutralization and therefore exhibit lower resiliencies and shorter distances. Comparative Examples 4 and 5 have total volumes of dimples that lie outside the range according to the invention. As a result, Comparative Example 4 cannot limit an uplifting trajectory, while Comparative Example 5 does so in excess and leads to the tendency of the ball to drop, both resulting in shorter distances.

Examples 1 to 4, however, have a cover made of ternary copolymer ionomer with higher degree of neutralization, and produced excellent results in both resilience and travel distance. Example 5 uses ternary copolymer ionomer with higher degree of neutralization for the intermediate layer, producing excellent results in both resilience and distance. Example 6 uses ternary copolymer ionomer with higher degree of neutralization for the center with excellent results in both resilience and distance. The results in Table 5 also indicate that ternary copolymer ionomer with higher degree of neutralization is used for the cover with better results in resilience than it is used for the center or the intermediate layer.

The present invention provides a center, an intermediate layer or a cover of a golf ball made of a composition with increased degree of neutralization of carboxylic acid in an ionomer composition to limit an uplifting trajectory of the golf ball that would cause the travel distance to be decreased, thereby preventing decrease in the distance against an opposing wind. The total volume of dimples of a golf ball is larger than usual to limit an uplifting trajectory of the ball (a larger drag coefficient), providing a trajectory in which the height of the golf ball is well retained in the latter half of the flight of the ball, thereby increasing the distance, providing a valuable golf ball that can meet needs of golfers.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

1. A golf ball formed of multiple layers, wherein at least one layer is made of a composition of a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound mixed together, at least 80% of a carboxyl group contained in the composition is neutralized, and a total volume of dimples (Dv) on a cover surface is 495-575 mm³.
 2. A golf ball formed of multiple layers, wherein a cover layer is made of a composition of a ternary copolymer ionomer, a higher fatty acid and an inorganic metal compound mixed together, at least 80% of a carboxyl group contained in the composition is neutralized, and a total volume of dimples (Dv) on a cover surface is 495-575 mm³.
 3. The golf ball according to claim 2, wherein the higher fatty acid is a higher fatty acid with 12-40 carbon atoms.
 4. The golf ball according to claim 2, wherein said higher fatty acid is selected from stearic acid or oleic acid, and a metal component of the inorganic metal compound is selected from the group consisting of Na, Zn, Mg, Ca, Li and K.
 5. The golf ball according to claim 2, wherein said cover is made of a composition with a Shore D hardness of 40-65.
 6. The golf ball according to claim 2, wherein a degree of neutralization of the carboxyl group contained in said composition is no less than 90%.
 7. The golf ball according to claim 2, wherein a degree of neutralization of the carboxyl group contained in said composition is 100%. 